This invention relates to a two-cycle diesel engine of the type commonly used in connection with models and other small devices.
The two-cycle diesel engine is known in the prior art and has been used, principally in Europe, in the flying model field for quite a number of years. This type of diesel engine provides a broad range of power while producing comparatively little noise. At the same time, it is very economical to operate. Basically, the principal difference between the operation of the diesel and that of the standard glow-plug engine is that the diesel does not employ a spark plug or glow plug to ignite the fuel. Instead, fuel combustion in the diesel occurs due to the heat created by the high compression of air within the engine.
Timing or rate of firing in the diesel is determined by the relative size of a variable combustion chamber. As the size of the combustion chamber is reduced from its maximum, the amount of heat is correspondingly increased, and the firing becomes more rapid until an optimum operational condition is reached. To accomplish this variation in the combustion chamber size, many of these types of prior art diesel engines employ a metal contra piston fitted in an engine cylinder above a piston. The contra piston in the prior art actually forms the top of the combustion chamber, and its position is adjustable with respect to the actual piston itself. The adjustment is usually made by a lever or a screw. Although the contra piston must be movable with respect to the piston to permit adjustment in the size of the combustion chamber, it must at the same time provide a good seal with the engine cylinder to prevent any gas leakage which would reduce compression and efficiency. This problem is further complicated by the fact that heat from engine operation will cause the contra piston to expand and a too closely fitted contra piston might become locked in place and be useless in adjusting the firing rate. Therefore, the contra piston in the prior art diesel engines and the corresponding engine cylinders must be machined very accurately to minute tolerances, and this is extremely expensive.
Conversion of the common glow plug or spark-ignition engine to a diesel engine has also been accomplished in the prior art. There, a cylindrical liner is installed inside an engine cylinder. The liner contains a close-fitting but movable contra piston which operates in the same manner as previously described to adjust the size of the combustion chamber. Again, expense is the major factor as the contra piston and the liner must be fabricated to extreme tolerances.
As a further drawback, most prior art two-cycle diesel engines have no built in safety feature to permit gas to escape should the engine severely overheat. Therefore, if this condition does occur, the expensive prior art diesel engine may explode or at least be extensively damaged.
Finally, due to their design characteristics, the displacement of these prior art diesel engines is considered to be very limited. This is because of the fact that as displacement increases, the amount of surface area in the combustion chamber also increases. Consequently, the heat loss from the combustion chamber through the surface area of the engine cylinder and contra piston becomes great. Efficiency is reduced, and the engine does not run smoothly.
Therefore, despite their performance advantages over the conventional glow-plug engine, because of their expense, unsafe operation possibilities and limited size, the prior art two-cycle diesel engines are not widely used in the United States.